Various functions for generating electric power in a nuclear reactor power plant require two critical resources, i.e., water and power. For example, water is used for cooling the fuel inside of the reactor and the spent fuel pool, and power is employed for a variety of plant functions including pumping, valve actuations, instrumentation and plant monitoring. During an accident scenario, such as station blackout, or other event resulting in the loss of all AC power, it may be difficult to obtain and provide external resources to the nuclear plant site to cope with the accident. Therefore, it is beneficial for the plant site to have alternate means to produce power and provide cooling water during a loss of AC power scenario.
In general, the Main Control Room Habitability System (VES) in a nuclear reactor power plant is a passively powered system which uses air to provide ventilation, cooling and filtration of the control room's environment following an accident or other event involving a loss of all AC power. FIG. 1 shows schematically a VES system 10 in accordance with the prior art. Compressed air is stored in tank 2 and pressurized. Typically, air is stored at a maximum pressure of 4000 psi. A minimum pressure of the tank is 3333 psi, with air at 60° F. under normal conditions. Further, it is typical for VES systems to employ more than one tank to store the compressed air. For example, in some commercial nuclear reactor power plants, such as the Westinghouse AP1000 plant, 32 tanks are used with each tank having a free volume of about 46.1 ft3. A stream of compressed air 4 is passed from the tank 2 through a pressure regulator 6. The minimum inlet pressure of the pressure regulator 6 is 200 psi. The pressure regulator 6 reduces the pressure of the stream of compressed air 4 such that a stream of lower pressure compressed air 8, which has a volumetric flow rate of 65 SCFM, passes through the outlet 7, is fed to an eductor nozzle 11 and is used to power an eductor 9. The air pressure at the outlet 7 is reduced to an intermediate pressure. For the AP1000 plant, the intermediate pressure, i.e., the pressure of the stream of lower pressure compressed air 8, is 120 psi. The flow fed to the eductor nozzle 11 provides fresh air for the control room and the eductor 9 provides for a circulation of airflow within the control room space 13.
For the AP1000, the compressed air stored in a nuclear reactor power plant is sufficient to provide 65±5 SCFM to the main control room area for at least 72 hours following an accident or other event involving a loss of all AC power. This compressed air represents a significant amount of potential energy.
It is known in the art to employ various passively powered designs, such as the VES, to mitigate accident events in a nuclear reactor without operator intervention or off-site power. These passively powered designs emphasize safety features that rely on natural forces, such as pressurized gas, gravity flow, natural circulation flow, and convection, and do not rely on active components (such as, pumps, fans or diesel generators). Further, passive systems are designed to function without safety grade support systems (such as, AC power, component cooling water, service water, and HVAC).
It is desired to develop further passive features and mitigation strategies for use in nuclear reactor power plants. For example, it is desired to recover energy from nuclear plant processes for use during accident and other event sequences when resources may not be readily available. Accordingly, this invention provides systems and methods for extracting significant useful energy from the compressed air in the VES. This energy may be employed in the nuclear plant to cope with accident and other loss of AC power event sequences wherein the VES is activated.